1. Field of the Invention
This invention relates to sensing apparatus and, more particularly, to sensing apparatus for mOnitoring the operation of alternating current powered devices.
2. History of Prior Art
A variety of systems have heretofore been developed to monitor the operation and/or status of electrically powered apparatus. For example, various types of test equipment, well known to those skilled in the art, have been developed to provide information as to both the instantaneous electrical activity of a circuit as well as its electrical activity over time. As a subset of the above, a variety of systems heretofore have been developed to monitor the operation of television sets. The purpose of some of these systems is to help collect data indicative of the popularity of particular television programs. The Nielsen rating system is an example of such a system. The purpose of other television set monitoring systems is to collect information regarding whether a hotel guest is watching a playing of a videotaped motion picture or similar program for which that guest is willing to pay. The Spectravision.RTM. Movie System, which brings recently-released guest-pay movies to hotel guests over their in-room televisions, is a prime example of one of these types of systems.
During the operation of the above-described systems, any number of a variety of parameters are sensed as part of the overall monitoring operations For example, the basic on-or-off state of the television set may be monitored and, in addition, when the television is on, exactly which channel has been selected by a viewer. Yet another parameter which may be monitored is the length of time that the television is on with a single, particular channel being selected for viewing. In the Spectravision.RTM. system mentioned above, for example, a cumulative timing circuit is employed to determine when a viewer has watched a pay channel for a predetermined period of time, e.g., five minutes, after which time other circuit elements cause a preselected charge to be added to the viewer's room bill. There are a multitude of other parameters, in addition to those mentioned above, that may be sensed in television operation monitoring systems.
In addition to parameter sensing circuits, television monitoring systems generally also include means for causing certain actions to occur based upon the results or outputs of the sensing circuits. In the Nielsen rating system, for example, data regarding the programs being watched on a particular television set in a selected household are forwarded to a central data collection point where the information is collected and tabulated to produce statistically correlated popularity ratings of each television program in different viewer markets. In the Spectravision.RTM. system, circuitry is included that disables the sensing of individual room movie selection keys when the television set in that room is turned off, thus ensuring that a hotel guest does not inadvertently select (and be billed for) a movie while the television is turned off.
The monitoring systems described above, while effective in many situations, have proven to have certain shortcomings. Many of these shortcomings relate to the fact that it is frequently desired to control certain responses based upon different levels of electrical activity, as opposed to situations in which there is either some electrical activity or there is not. The latter situation would exist, for example, when different desired responses would be actuated depending upon whether a television set was either on or off. This is a fairly easy condition to sense. The former situation, i.e., where it is desired to detect subtle differences between levels of electrical activity, is one in which the shortcomings of prior art monitoring systems have been particularly noticeable. For example, certain portions of recent vintage hotel television sets (e.g., warm-up circuitry and/or built-in clocks, radios and similar apparatus) are always operational and/or are independently operational of the audio/video portion of the television set. These circuits may either continue to operate or can even become disabled when the television receiving circuitry is activated by a user for viewing. Thus, most hotel in-room television sets are never simply on or off; rather, there are various levels of electrical activity based upon which circuits within the set are operating.
Simply put, a shortcoming of prior art television monitoring systems is that they have not been able to produce effective status responses in cases in which a television system has a variety of electrical operational levels and the particular desired response differs depending upon the particular level at which the television system is operating.